The present invention relates to a load handling clamp for use with a forklift or other load handling vehicle and, more particularly, to a load handling clamp having a regenerative hydraulic circuit.
Clamp attachments are used on forklift trucks and other load handling vehicles to engage a variety of loads. For example, rolls of paper are commonly engaged and moved with hydraulically actuated paper roll clamps attached to forklift trucks. The forklift truck is maneuvered to locate the paper roll between a pair of clamp arms and when the roll is in the proper position one or more hydraulic actuators are activated to clamp the roll between contact pads at the foremost ends of the arms. Paper rolls commonly weigh in excess of 1000 kilograms (kg.) and the clamp must generate and maintain sufficient clamping force to provide the necessary friction between the contact pads and the paper roll to immobilize the load in the clamp. On the other hand, the clamping force must be controlled to avoid distorting the clamped load or damaging the surface of the load in contact with the clamp. Some lighter loads are particularly fragile and the clamping force must be limited to a fraction of the force that can normally be exerted by the clamp. Clamping force can be reduced by controls that reduce the hydraulic pressure in the actuator(s) but if the pressure is too low the clamp may operate slowly or not at all. The clamping force can also be reduced by reducing the dimensions of portions of the hydraulic actuator but it is expensive to design, manufacture and stock special hydraulic actuators and reducing the size of portions of an actuator may weaken it structurally making the actuator prone to damage during use.
What is desired, therefore, is a hydraulically actuated clamp with a substantially reduced clamping force but which includes few custom components, is structurally rugged and which operates quickly and reliably.